1. Field of the Disclosure
This disclosure relates in general to a process for making an electronic device. It further relates to the device made by the process.
2. Description of the Related Art
Electronic devices utilizing organic active materials are present in many different kinds of electronic equipment. In such devices, an organic active layer is sandwiched between two electrodes.
One type of electronic device is an organic light emitting diode (OLED). OLEDs are promising for display applications due to their high power-conversion efficiency and low processing costs. Such displays are especially promising for battery-powered, portable electronic devices, including cell-phones, personal digital assistants, handheld personal computers, and DVD players. These applications call for displays with high information content, full color, and fast video rate response time in addition to low power consumption.
Current research in the production of full-color OLEDs is directed toward the development of cost effective, high throughput processes for producing color pixels. For the manufacture of monochromatic displays by liquid processing, spin-coating processes have been widely adopted (see, e.g., David Braun and Alan J. Heeger, Appl. Phys. Letters 58, 1982 (1991)). However, manufacture of full-color displays requires certain modifications to procedures used in manufacture of monochromatic displays. For example, to make a display with full-color images, each display pixel is divided into three subpixels, each emitting one of the three primary display colors, red, green, and blue. This division of full-color pixels into three subpixels has resulted in a need to modify current processes to prevent the spreading of the liquid colored materials (i.e., inks) and color mixing.
Several methods for providing ink containment are described in the literature. These are based on containment structures, surface tension discontinuities, and combinations of both. Containment structures are geometric obstacles to spreading: pixel wells, banks, etc. In order to be effective these structures must be large, comparable to the wet thickness of the deposited materials. When the emissive ink is printed into these structures it wets onto the structure surface, so thickness uniformity is reduced near the structure. Therefore the structure must be moved outside the emissive “pixel” region so the non-uniformities are not visible in operation. Due to limited space on the display (especially high-resolution displays) this reduces the available emissive area of the pixel. Practical containment structures generally have a negative impact on quality when depositing continuous layers of the charge injection and transport layers. Consequently, all the layers must be printed.
In addition, surface tension discontinuities are obtained when there are either printed or vapor deposited regions of low surface tension materials. These low surface tension materials generally must be applied before printing or coating the first organic active layer in the pixel area. Generally the use of these treatments impacts the quality when coating continuous non-emissive layers, so all the layers must be printed.
An example of a combination of two ink containment techniques is CF4-plasma treatment of photoresist bank structures (pixel wells, channels). Generally, all of the active layers must be printed in the pixel areas.
All these containment methods have the drawback of precluding continuous coating. Continuous coating of one or more layers is desirable as it can result in higher yields and lower equipment cost. There exists, therefore, a need for improved processes for forming electronic devices.